Rick Cruse, Greg Brenneman, and Matt Helmers Iowa Water Center and Iowa State University Extension

For a Given Water Application Rate - Runoff Caused By Surface of sponge restricting water infiltration – paper towel covering sponge Sponge full of water – nowhere for water to go

For a Given Sponge Condition – Runoff Caused by Increased water application rate

Infiltration Infiltration – entry of water into the soil. Influenced by: Physical characteristics of the soil (e.g. soil texture and soil structure) Soil moisture Cover on the soil and management of the soil Rainfall intensity

Impacts of Land Use on Infiltration Source: Bharati et. al., 2002

Landuse Example Pochohantas Co. Watershed

Changes in Iowa Farmland

Land Cover Trends More row crops Row crops have lower infiltration rates

Tile Drainage Removes water from saturated ‘sponge’ Creates storage space for subsequent rainfall Reduces runoff for repetitive storms when soil profile is full or nearly full

Trends in Precipitation Groisman, Pavel Ya., Richard W. Knight, David R. Easterling, Thomas R. Karl,Gabriele C. Hegerl, and Vyacheslav N. Razuvaev Trends in intense precipitation in the climate record. J. of Climate. 18:

Cedar River Annual Flow Cedar Rapids

Cedar River Peak Flow Rates

Iowa River Peak Flow Rates

Iowa River Peak Flows - Marengo

Concluding Comments Loss of continuous living cover, increased soil disturbance, and limited use of conservation practices can increase runoff Impacts are greater for smaller events and dryer soils Much smaller impacts for larger events or wet soils Removal of water from soil profile (evapotransporation, tile drainage) reduces runoff Water runs off concrete, asphalt, and building roofs Extreme rainfall event frequencies have increased High production and increased water infiltration (10% perennial cover) may coexist